''' NEEDS TESTS '''

import operator
from functools import reduce

from registrasion.models import commerce
from registrasion.models import inventory

from collections.abc import Iterable
from collections import namedtuple
from django.db.models import Case
from django.db.models import Q
from django.db.models import Sum
from django.db.models import When
from django.db.models import Value

_ProductAndQuantity = namedtuple("ProductAndQuantity", ["product", "quantity"])


class ProductAndQuantity(_ProductAndQuantity):
    ''' Class that holds a product and a quantity.

    Attributes:
        product (models.inventory.Product)

        quantity (int)

    '''
    pass


class ItemController(object):

    def __init__(self, user):
        self.user = user

    def _items(self, cart_status, category=None):
        ''' Aggregates the items that this user has purchased.

        Arguments:
            cart_status (int or Iterable(int)): etc
            category (Optional[models.inventory.Category]): the category
                of items to restrict to.

        Returns:
            [ProductAndQuantity, ...]: A list of product-quantity pairs,
                aggregating like products from across multiple invoices.

        '''

        if not isinstance(cart_status, Iterable):
            cart_status = [cart_status]

        status_query = (
            Q(productitem__cart__status=status) for status in cart_status
        )

        in_cart = Q(productitem__cart__user=self.user)
        in_cart = in_cart & reduce(operator.__or__, status_query)

        quantities_in_cart = When(
            in_cart,
            then="productitem__quantity",
        )

        quantities_or_zero = Case(
            quantities_in_cart,
            default=Value(0),
        )

        products = inventory.Product.objects

        if category:
            products = products.filter(category=category)

        products = products.select_related("category")
        products = products.annotate(quantity=Sum(quantities_or_zero))
        products = products.filter(quantity__gt=0)

        out = []
        for prod in products:
            out.append(ProductAndQuantity(prod, prod.quantity))
        return out

    def items_pending_or_purchased(self):
        ''' Returns the items that this user has purchased or has pending. '''
        status = [commerce.Cart.STATUS_PAID, commerce.Cart.STATUS_ACTIVE]
        return self._items(status)

    def items_purchased(self, category=None):
        ''' Aggregates the items that this user has purchased.

        Arguments:
            category (Optional[models.inventory.Category]): the category
                of items to restrict to.

        Returns:
            [ProductAndQuantity, ...]: A list of product-quantity pairs,
                aggregating like products from across multiple invoices.

        '''
        return self._items(commerce.Cart.STATUS_PAID, category=category)

    def items_pending(self):
        ''' Gets all of the items that the user has reserved, but has not yet
        paid for.

        Returns:
            [ProductAndQuantity, ...]: A list of product-quantity pairs for the
                items that the user has not yet paid for.

        '''

        return self._items(commerce.Cart.STATUS_ACTIVE)

    def items_released(self):
        ''' Gets all of the items that the user previously paid for, but has
        since refunded.

        Returns:
            [ProductAndQuantity, ...]: A list of product-quantity pairs for the
                items that the user has not yet paid for.

        '''

        return self._items(commerce.Cart.STATUS_RELEASED)